Effect of draw ratio on the actuation performance of twisted polymer artificial muscles

Abstract Twisted polymer artificial muscle is a promising low-cost soft actuation that can mimic natural muscles by sensing external stimuli and generate torsional deformation. Here, we investigate the effect of draw ratio on the torsional actuation performances of twisted Nylon-6 fiber from an experimental and theoretical perspective. Experiments show that increasing the draw ratio enhances the fiber orientation and significantly increases Young’s modulus and shear modulus. The thermal anisotropy of the precursor fiber and the recovered torque generated by twisted fiber increase dramatically with increasing draw ratio. The Yang-Li thermal-mechanical actuation model is used to predict the torsional actuation performance of twisted fiber with different draw ratios. The theoretical predictions of recovered torque align well with the experimental results. Analysis of stress distributions within the cross-section of the twisted fiber shows that the higher draw ratio results in larger stress. This study sheds light on the structural optimization design of thermally-activated artificial muscles.